Organic rankine cycle and steam turbine for intermediate temperature waste heat recovery in total site integration

The utilization of waste heat for heat recovery technologies in process sites has been widely known in improving the site energy saving and energy efficiency. The Total Site Heat Integration (TSHI) methodologies have been established over time to assist the integration of heat recovery technologies in process sites with a centralized utility system, which is also known as Total Site (TS). One of the earliest application of TSHI concept in waste heat recovery was through steam turbine using the popular Willan's line approximation. The TSHI methodologies later were extended to integrate with wide range of heat recovery technologies in many literatures, whereby Organic Rankine Cycle (ORC) has been reported to be the one of the beneficial options for heat recovery. In general, the medium to high temperature waste heat is recovered via condensing/backpressure steam turbine, whereas ORC is targeted for recovering the low temperature waste heat. However, it is known that condensing turbine is also abled to generate power by condensing low grade steam to sub-ambient pressure, which is comparable with ORC integration. In this work, the integration of ORC and condensing turbine was considered for a multiple-process system to recover intermediate temperature waste heat through utility system. This study presented a numerical methodology to investigate the performance analysis of integration of ORC and condensing turbine in process sites for recovering waste heat from a centralized utility system. A modified retrofit case study was used to demonstrate the effectiveness application of the proposed methodology. The performances of ORC and condensing steam turbine were evaluated with the plant total utility costing as the objective function. The turbine integration was found to be more beneficial in the modified case study with lower utility cost involved. However, the capital cost has not been considered in the analysis.